Grafting looks like carpentry and behaves like surgery. Two cut surfaces are pressed together and, if everything goes right, they stop being two plants. What happens in between is worth understanding, because almost every decision a propagation house makes in those four weeks is a decision about that process — and almost none of it is visible while it is happening.
The join is made by a layer most people never see
Just under the bark of a stem is a thin sleeve of dividing cells called the cambium. It is the only tissue in the stem that makes new cells. Everything a graft becomes, it becomes from there.
When you cut a scion and a rootstock, you expose a ring of cambium on each. Press the two together and the cells nearest the wound start dividing into a disorganised mass called callus — undifferentiated tissue, the plant equivalent of a scab that keeps growing. Within that callus, new cambium forms, and it forms across the gap. Once the new cambium is continuous from the rootstock into the scion, the two are one plant: water can move up, sugars can move down.
Two things follow from this that matter on a bench.
First, alignment is about the cambium, not about the stems. A scion sitting neatly centred on a thicker rootstock can have almost no cambial contact. A scion pushed to one side of a mismatched rootstock can have plenty. If the diameters differ, favour one edge.
Second, the callus is fragile for longer than it feels. It is not a scar; it is actively dividing tissue with no strength of its own. Movement at the join tears the new cells apart faster than they can be replaced, which is why a sleeve that lets the join shift is worse than one that grips a little firmly.
Rose is done differently, and that changes everything
In most grafting, the rootstock is a plant that already has roots. In commercial rose propagation it usually is not. A cutting is taken and grafted in the same operation, so the join knits while the rootstock is still forming its own roots underneath. The technique has a name — stenting — and it was developed for exactly this: getting a saleable young plant in one pass instead of two.
It also means the graft is being asked to do two hard things at once, with nothing underneath it. The plant cannot yet draw water through the join, and it cannot yet draw water from the medium either. Its only defence against drying out is the air around its leaves, which is why the mist is not optional and why the sleeve is doing structural work for the whole period.
What the four weeks look like
Days 0 to 2. Nothing useful is happening yet. The cut surfaces are wounded, and the plant is losing water it cannot replace. Everything you do here is about keeping the leaf surface damp and the wound clean.
Days 2 to 7. Callus forms. This is the period where a loose sleeve costs you, because the tissue bridging the gap is new every day and movement destroys it.
Days 7 to 14. New cambium differentiates within the callus and the vascular connection begins. Somewhere in this window the plant starts to be able to move water through the join, which is the first point at which misting can be eased at all.
Days 14 to 21. Roots initiate at the base while the join is still consolidating. Both processes want warmth and moisture; the roots also want oxygen, which is where a waterlogged cell base quietly undoes the work.
Day 28. Take is assessed. The working definition used in Kenyan rose research is the presence of both a shoot and roots at four weeks — not a shoot alone, which can persist for a while on stored reserves and then collapse.
The losses are not where people look
Growers tend to blame the cut. In practice the cut is the part the bench does most consistently, because it is the part someone is watching. The losses cluster in three less visible places.
Uneven medium. A tray filled a few millimetres short across one end has less root volume at that end, and it finishes days behind. Nobody sees it until the count.
Sleeve fit. A bore one size over lets the join move for four weeks. A bore one size under presses on the cambium — the exact tissue that has to divide. Either way the loss looks like “poor take” rather than like a purchasing decision.
The base of the cell. Misting keeps the leaves wet and also keeps putting water into the medium. If the cell base cannot drain, the roots that were about to form suffocate while the top of the plant looks perfectly healthy.
What the numbers look like in Kenya
Published Kenyan work gives a sense of how much the controllable variables matter. In a study of the rose variety ‘Inca’ by Otiende, Nyabundi and Ngamau (Journal of Applied Horticulture, 18(1), 2016), grafting take on Natal Briar rootstock reached 85.2 % using cuttings taken from low on the mother shoot, while ‘Rosa Progress’ averaged 60.0 % across the trial. Cuttings from the base of the shoot beat cuttings from the top on both rootstocks, and auxin-treated cuttings beat untreated.
That is one trial, one variety, one set of conditions — not a benchmark for your house. What it does show is the scale: the gap between a considered choice and a careless one at this stage is measured in tens of points, not in fractions.
The practical summary
Hold the join absolutely still for four weeks. Keep the leaf wet and the cell base drained, which are opposing requirements and the reason this stage is hard. Match the sleeve to a stem you have actually measured. And assume nothing is visible until day 28, because it is not.